IL7R and severe combined immunodeficiency: Nineteen known inborn errors of immunity cause SCID by affecting T cell commitment at the early progenitor stages (e.g., IL7R, IL2RG, and JAK3), T cell survival (e.g., AK2, ADA, and RAC2), T cell receptor (TCR) recombination (e.g., RAG1, RAG2, LIG4, PRKDC, DCLRE1C, and NHEJ1), and pre-TCR/TCR signaling (e.g., CD45, CD3D, CD3E, CD3Z, SLP76, LAT, and CORO1A) (3).